The background description set out below represents a description of the background to the present invention and therefore does not necessarily constitute prior art.
Combustion engines, e.g. those of vehicles or watercraft, are powered by fuels such as diesel, petrol, ethanol or mixtures of such fuels with one another and/or with additives of various kinds. The fuel is provided to the combustion engine by a fuel system comprising inter alia one or more fuel tanks and devices which convey the fuel from the fuel tanks to the combustion engine.
The devices which convey the fuel to the engine may for example comprise lines for transferring the fuel within the vehicle, one or more pumps, which may be divided into respective low-pressure and high-pressure circuits, filters, connections and other devices for fuel transfer. The fuel is injected into the engine's cylinders by a fuel injection system which comprises one injection means, also called injector, per cylinder. The injection means may for example be provided with fuel by a common-rail unit which provides pressurized fuel to all of the injection means, or by separate units with pressurized fuel for the respective injection means.
In the engine's cylinders the fuel is burnt, thereby creating a torque which is provided by the engine via its output shaft.
It is important for many systems in, for example, a vehicle that an engine of the vehicle be provided with an expected/demanded torque. The expected/demanded torque usually corresponds here to a torque demanded from the engine. There is for example a risk that automatically effected gearchanges in a gearbox may take place in a non-optimum way if the torque provided by the engine differs from the torque which the gearchange system expects the engine to provide. Systems for cruise control of the vehicle will base their control of the engine on an expected torque provided, which means that the cruise control also risks becoming non-optimum if an unexpected torque is provided by the engine. A non-optimum cruise control most often results also in unnecessarily high fuel consumption and hence also in unnecessarily high discharges of exhaust gases from the vehicle.
There may be various reasons why the torque provided by the engine does not correspond to the torque expected to be delivered by the engine.
One reason for an unexpected torque being delivered may be that a fuel with an energy content which differs from an expected energy content is used to power the engine. For example, a fuel with a lower energy content, e.g. some kind of bio-diesel, may be used in the vehicle despite the vehicle's systems being set such that a fuel with a higher energy content, e.g. fossil diesel, is being used. If, for example, FAME (fatty acid methyl ester) is used to power the engine when the systems is set for fossil diesel being used, the power output and the torque provided by the engine will likely decrease, in some cases by up to about 10 percent.
Another reason for an unexpected torque being delivered may be that no fuel is being injected into the cylinders because of a fuel stoppage in the fuel system. Fuel stoppages may occur for various reasons in various ways. Faults and/or damage may for example occur in the fuel tanks, in the devices which convey the fuel from the fuel tanks to the engine and/or in the fuel injection system. When there is a stoppage in the fuel supply to the engine, the engine will provide no propulsive torque. There is therefore an obvious risk that engine stoppage may for example occur during a gearchange if the gearchange system thinks that a certain torque is provided by the engine when the actual torque provided is nil.